Recovery of volatile solvents



Feb. 10, 1948. w. P. HEYboRN RECOVERY OF VOLATILE SOLVENTS Filed April 30, 1945 Patented Feb. 10, 1948 2,435,781 RECOVERY OF VOLATILE S OLVEN TS William P. Heydom, Akron, Ohio, assignor to Wingfoot Corporation, Akron, Ohio, a corporation of Delaware Application April 30, 1945, Serial No. 591,108 7 Claims. Cl. 183-49) This invention relates to a method of recovering volatile solvent vapors from air or other gas mixtures. It particularly relates to a method of preventing corrosion ln solvent recovery apparatus,

especially when used to separate chlorine-substituted hydrocarbons from air by an adsorption technique.

In the conventional solvent recovery practice, the air or other gas containing small amounts of the volatile organic solvent is passed through a porous body of activated carbon which adsorbs the molecules of organic solvent. After the activated carbon is saturated, the adsorbed vapors are evolved by heating or steaming the carbon and the concentrated vapors thereby obtained are condensed by cooling. The activated carbon beds, which may be several inches to two or three feet in thickness, are generally disposed in ahorizontal position and the air passed downwardly through the relatively thin layers of carbon to minimize the resistance to the passage of the gas stream. The bed is usually supported in a closed chamber and the air stream directed in such a manner so that all of the gas is passed through the body of carbon. It is customary to support the activated carbon bed with thin metal plates. preferably of a corrosion-resistant metal, such as Monel. The metal plate is supported by structural members of the same or similar corrosionresistant metal. The organic solvents are corrosive, especially at the normal adsorbing temperature of 100 to 150 F. The activated carbon appears to catalyze the corrosion and the intermittent steaming further promotes the oxidation of the metallic structures. In ordinary practice it is frequently necessary to repair or replace the supporting plate after. ten days of continuous operation.

The principal object of this invention is to provide an economical method of recovering volatile solvents by adsorption on activated .carbon through the elimination of the frequent interruptions of operation for replacing the carbon-supporting structures. A further purpose of the invention is to minimize the loss of activated carbon by the passage of carbon through the perforated plate, especially after the perforation are enlarged by corrosion.

In accordance with this invention, theactivated carbon is supported by a porous layer of integral shapes of an inert non-absorptive material which ofiers little resistance to the passage of the gases being stripped of solvent vapors. The said porous layer is supported by the perforated plate or grating containing interstices smaller than the diameter of the integral shapes in the lower part of the porous bed. Thus, the activated carbon is supportedwithout contacting the metal grating. A preferred modification of the invention involves the use of a porous bed containing integral shapes of stoneware or ceramic material which vary in size from large shapes at the bottom to shapes approximately the size of the activated carbon granules at the top. The graduated bed provides a rigid support for the activated charcoal without permitting the carbon particles to fall through and contact the metallic supporting structures. If desired the thin metal plate may be entirely eliminated and a coarse grating, having openings slightl smaller than the integral stoneware shapes at the bottom of the porous bed, used to support the adsorbing bed.

Many types of packing are available commercially in various sizes. For example, Berl saddles or Raschig rings may be advantageously used for the lower part of the porous layer. The uppermost layers may utilize granular materials of approximately the size and shape of the activated carbon granules. If desired, the first layer of activated carbon may be of larger particle size, thereby avoiding the necessity of using a granular non-adsorbing material. A very effective adsorbing bed may be prepared by using three difie'rent sizes of Berl saddles ranging from 1%" to /2" in size, superposed with about a, one-inch layer of a. very coarse activated carbon having a particle size of about /4" to /2" in diameter. Such a porous bed will support the commercial adsorbing carbon without permitting any to filter through to the metal structure.

The nature of the corrosion is not fully understood, but is believed to be an electrolytic phenomenon, probably induced by the contact of dissimilar materials in the presence of an electrolyte.

Fig. l is a longitudinal section of the apparatus employed.

Fig. 2 is an end view of the same.

The accompanying drawing demonstrates one method of practicing the invention. The adsorptive bed is entirely enclosed within a container In into which the gas to be stripped is passed through gas inlet 1 into a diffuser 6 which insures an even distribution within the container l 0. The activated carbon bed 9 is superposed on the inert porous bed 8 which rests on the perforated plate or grating I. The entire structure rests on a series of parallel bars I I. The space between the container walls Ill and the adsorbing bed are sealed by structures 5 which direct all gases downwardly through the carbon bed 9, the inert porous layer 8 and the supporting plate or grating l. The air or other gas stripped of solvent vapors is drawn ofi through the exit 2. The adsorber is provided with a steam inlet 3 for the purpose of desorbing the carbon. The vent 4 is used to draw off the desorbed solvent, and steam which are condensed and the immiscible liquids separated fromeac h other.

If desired, the apparatus may ,be used by introducing the solvent-laden gases through opening 2, passing them upwardly through the metallic grating l, the porous layer 8, the activated carbon bed 9 and out through opening I'.

Further details of a specificinethod of perat; ing the new invention WillLbB a rent'from the following example. u

Sixteen thousand cubic feet per minute of air containing small proportionsof ethylenedichloride was passed through a bed of 101109 lbs. of activated carbon, '7' 6'. in width and 28' 9" in length and about l8 toZO inches in thickness.

Th c bo was ported by a pq s or tled Mariel as r a n i il l e s th e es of L /z' Berl saddles, one chof l' Berl a M 1 f es a t ated. h c a 'F bed became saturated with fsolvent fin '50 minutes. Upon steaming and condensing, approximately .one" .hundredfgallons Iof liquid diethyl ene chlofreeware recovered, representing 385% of' -the solvent ;in the airstreain. hAitersix'rnonths .of continuous operation, 'i tlie adsorbing structure was examined and found to requirer' o repairing. :A previously used structure, in which the granular activated eharcoal rested vup 1Irtiifeper- J, a

IoratedIMonel rnetaI plate without the interve flins v bb on-a i qrbent hap r u e e first repairs after ten days of use and subsequent repairs at the rate of about two to three ,per

w erenm at the end of sixty .days the entire supporting structure had to bereplaced.

although the invention has been described with respect to a spBCific example, it is .not intended that the details thereof shall be .construedas limitations on the scope of the invention except to the extent included in tl1e,fo1lowingclaims.

I claim:

1. An adsorbing bed for the recovery of volatile organic liquid vapors which comprises a horizontally disposed metallic member having a plurality of transversejapertures therein, aporous layer of integral. shapes of a ceramic material superposed on said metallic member and a layer of granular activated carbonsuperposedon said porous layer of integral shapes.

. 2. An adsorbing bedfor the recovery of volatile organic liquid vapors which comprises a horizontally disposed metallic plate ha'vinga plurality of uniformly spaced apertures therein, a porous layer of shapes of ceramic superposed on T said plate, and a layer of granular activated carbon superposed on' said porous layer, said porous layer. "being comprised 'of integral shapes of a ceramicv material and graduated in size from slightly larger than said aperturesfat the plate to. approximately thesize of th activated carbon granules at the surface in contact with the carban.

3. An adsorbing bed for the recovery of volatile organic liquid vapors which comprises a metallic grating, a layer of integral shapes of an inert material superposed on said grating, the integral ceramic shapes being of a size and shape that ,will not pass throughlthe interstices of the grate, a layer of smaller integral ceramic shapes of an inert material superposed on the said first layer, and a layer of granular activated charcoal superposed on said layer of smaller integral shapes;

,4. An adsorbing bed for the recovery of volatile ,organic-liquid-vapors which comprises a body of granular activated carbon horizontally disposed on a supporting structure having a metallic'gratingj a porous layer of ceramic shapes superposed on said grating and a layer of activated carbon of a particle size two to five times t e aver e-d am ers the pa t pl n t s body of granular activated carbon superposed on h sa d w s lev r sa d ser s i r layer bein comp d c in eera ha graduated n size from the shapes in .cgntactwith the ratin which are large enough to be retained on the metallic grating to shapes in the upper-surface of the said porous inert layer which are small enoughito' provide adequate support for theparticles of ,largersized activated carbon.

5. In an adsorption bed for the recovery of volatile organic liquid vapors having a, body of granular activated charcoal supported by a .metallicscreen, the improvement .wlichconsists in a layer of integral shapes v.101 ceramic material inserted between the body of activated carbon and the metalscreen.

6. In an adsorption bed -for thes-recover-y of vapors of chlorine-substituted hydrocarbons, which bed is comprised of a body of granular activated carbon supported by a nietal lic screen, the improvement which consists in 'a layer of integral shapes of ceramic material between the body of activated carbon and the metallic screen.

7. In an adsorption bed for the recovery of vapors of chlorine-substituted hydrocarbons, which comprises a horizontally disposed metallic member having a plurality of transverse aper tures therein, a porous-layer of' integral shapes of e mi m r rrfis E as means member, and a aye-er granuiar activated car,- bon s e ns 2 sa d. nqr e'la r 9 integral ap f, I

F EN S The following references are of record the ale th s Pa e Germany Ju e 1 0, 233

Certificate of Correction Patent No. 2,435,781. February 10, 1948.

WILLIAM P. HEYDORN It is hereby certified that error appears in the printed specification of the above numbered patent requlrmg correction as follows:

Column 3, line 61, claim 2, after the Word ceramic insert material;

and that the said Letters Patent should be read with this correction therein that the same may conform to the record of the case in the Patent Oflice.

Signed and sealed this 1st day of March, A. D. 1949.

THOMAS F. MURPHY,

Assistant Commissioner of Patents. 

